Who is Participating?

SMTP is a unique property of Active Directory. As long as nobody else (a group, folder, new user) would need that address, there is no real issue.

Also note that all of the addresses assigned to an object are visible when that object is viewed from outlook.

Aliases are set in the ProxyAddresses property of the object in active directory. You could create a script that could update this, reading in a text file. If you are not programmatically inclined, Dovestones software has a package (ADBulkUsers) Which can create users or modify users if they already exist and this is one of the properties it can change.